1. Technical Field
The present disclosure relates to systems and methods for managing camshaft torsional loading in internal combustion engines having one or more camshaft driven engine accessories, such as a fuel pump or water pump.
2. Background Art
An internal combustion engine camshaft may be used to drive various engine accessories or auxiliary equipment, such as a fuel pump or water pump in addition to the intake or exhaust valves it actuates. Engines that use fuel at high pressure, such as direct injection engines and/or those using a single high-pressure fuel pump to supply all engine cylinders, often stroke the fuel pump plunger multiple times for every revolution of the camshaft. As such, the camshaft includes a cam with as many lobes as the number of strokes required by the fuel pump or other auxiliary device to provide the desired pressure and flow characteristics. Depending upon the particular valvetrain and engine configuration, optimal indexing or phasing between the cam lobes actuating the intake/exhaust valves and the cam lobes actuating the auxiliary device(s) may not be possible resulting in uneven or unbalanced torsional loading of the camshaft. This may adversely impact various other engine components, such as the camshaft chain drive system, for example. In addition, such torsional loading may contribute to undesirable noise, vibration, and harshness.
Various types of devices have been used to reduce the unbalanced torsional loading of the camshaft associated with intake/exhaust valve actuation. For example, U.S. Pat. No. 5,040,500 and French Pat. No. 2688563 disclose a balancing mechanism that operates on a dedicated cam to moderate dynamic loading associated with valve actuation. The present disclosure recognizes the desirability of managing torsional loading of the camshaft associated with actuation of an auxiliary device, such as a fuel pump, in addition to the loading associated with the intake or exhaust valves it actuates, especially in a configuration where the valve actuation and auxiliary device stroking cannot be phased to balance each other.